1. Field of the Invention
The present invention relates to a one shot mouldable and curable homogeneous rubber composition having a high Young's modulus, and more particularly to a rubber composition consisting mainly of polyisoprene rubber and a monomer mixture composed of divinylbenzene and .alpha.-methylstyrene, which has a high Young's modulus, a high tear energy .tau. and a high tensile strength retension at high temperature in the cured state.
2. Description of the Prior Art
Conventional rubber compositions composed of rubber and various compounding ingredients have a low Young's modulus, and when it is intended to use the rubber composition in a portion, wherein a high mechanical strength is required, it has been necessary to use the rubber composition in the form of a laminate combined with fibers and other reinforcing materials.
However, it is troublesome to effect laminating and moulding, and moreover, the resulting moulded articles are often poor in the homogeneity.
The present invention provides a one shot mouldable homogeneous rubber composition having all of the above described excellent physical properties. Moulded articles prepared from the rubber composition of the present invention have a sufficiently high mechanical strength without the use of reinforcing materials, such as fibers and the like, and are low in the permanent strain and excellent in the low-temperature characteristics and in the airtightness, and further are inexpensive.
There have been known several one shot mouldable rubber compositions composed of specifically limited rubber and specifically limited monomer. For example, U.S. Pat. No. 3,313,545 discloses a method wherein a rubber composition composed of cis-1,4-polybutadiene, divinylbenzene, silica and dicumyl peroxide and the like is heated and cured. There is a description in the U.S. Patent that the cured rubber obtained in this method is used as a material for solid golf ball. However, the cured rubber has an extremely high Young's modulus and an extremely low elongation and tear energy .tau.. That is, in the cured rubber, characteristic properties inherent to rubber are lost, and the rubber cannot develop fully performances as an elastomer. A method, wherein a rubber composition composed of polyisoprene rubber, styrene, divinylbenzene and an organic peroxide is heated and cured, is disclosed, for example, in Japanese Patent Application Publication No. 8,294/57, but the cured rubber has a very low tear energy .tau. over a wide range of rubber/monomer ratio and is poor in various performances at high temperature. Further, a method, wherein a rubber composition composed of polyisoprene rubber, trimethylolpropane trimethacrylate, sulfur and an organic peroxide is heated and cured, has been known (Preprint of "Problems in Recent Rubber Technics", Pages 5-19, (1972), Japan Chemical Engineering Union). However, the resulting cured rubber is very low in the Young's modulus and tear energy .tau..